1. Field of the Invention:
This invention relates to an optical system for a video camera, a television camera, etc. and, more particularly, to an optical system for the imaging apparatus using a color separation prism.
2. Description of the Related Art:
In the color television camera, the light beam having passed through the objective lens is split into three parts of different colors, i.e., red, green and blue, by the color separation prism, and their images are formed on the respective image pickup elements, from which a color signal is obtained.
Since the objective lens has usually a lateral chromatic aberration, the images for the different channels delicately differ in size from one another. This leads to a phenomenon that the three color images on the television display fail to exactly coincide with one another, that is, the so-called registration error is produced. In the conventional camera employing the image pickup tube, the registration error can be removed by electrically controlling the deflection of the electron beams in accordance with the lateral chromatic aberration the used lens has.
In recent years, however, the solid-state image pickup element has found its use in a rapidly increasing numbers of cameras. Since, in this case, the three elements are arrayed in a fixed geometry, the conventional way of correcting the registration can no longer be employed. Therefore, the lateral chromatic aberration of the objective lens reveals itself on the television display. Because of this, color deviation takes place in the margin of the display, causing the image quality to deteriorate.
From this reason, the objective lens for the camera using the solid-state image pickup elements must be better corrected for lateral chromatic aberration than was heretofore accepted. Hence, there are tendencies to use very expensive glasses of high extraordinary partial dispersion, and of increasing the number of constituent lenses while ignoring the increase of the size of the entire optical system.
As related art, mention may be made of those disclosed in U.S. Pat. Nos. 3,802,763 and 3,976,363.